1. Field of the Invention
This invention relates to a device for hoisting a load through a linear path and more particularly to an articulated connection of links drivingly connected to attain a multiplication of angular movement while maintaining a load in a preselected attitude movable through a linear path.
2. Description of the Prior Art
Camera dollies as disclosed in U.S. Pat. Nos. 3,168,284; 3,915,429 and 4,360,187 are well-known in the art and utilize articulated linkages mounted on mobile carriages or frames with power actuating means for initiating upward and downward pivotal movement of the linkage to move a camera platform. A preselected camera attitude is maintained while the camera platform is moved in a substantially linear path. The basic lifting mechanism is based on a conventional scissor type work platform in which one or more load lifting links are connected end-to-end to extend from the base to the camera platform on which the camera is positioned.
The earlier approaches to articulated camera dollies utilized hoisting devices that were substantially complex, requiring a relatively large mobile frame for positioning the camera. Consequently these hoisting devices were difficult to maneuver which limited their versatility in supporting cinematicographic and television cameras.
Articulated linkages for raising and lowering a platform in a substantially linear path for industrial uses are disclosed in U.S. Pat. Nos. 2,616,768; 3,363,474; 3,401,568; 3,415,021; 3,743,049; 4,019,604; 4,026,519; 4,056,198; and 4,299,533. These devices were not readily adaptable to camera hoists which were required to be smaller in scale with a shorter wheel base to provide greater flexibility in maneuvering the camera.
U.S. Pat. No. 4,360,187 discloses a hoisting device having a compact design that includes a dolly-like base on which is pivotally supported a primary hoist link rotatable about a fixed shaft upon actuation of a piston cylinder assembly. A final hoist link is pivotally connected and spaced in lateral relation to the distal end of the lower or primary link by the provision of an intermediate connection designed to transmit angular movement of the primary link into angular movement of the final or upper link having a magnitude equal to the magnitude of angular movement of the primary link. In the fully retracted position the primary and final links are positioned in adjacent parallel relation on the dolly.